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The gas generator includes, a housing having a gas discharge port, a first
combustion chamber defined by the housing, a first gas generating agent
adapted to generate gas to inflate an air bag, the first gas generating
agent having a first combustion temperature and disposed in the first
combustion chamber, a second gas generating agent adapted to generate gas
to inflate the air bag, the second gas generating agent having a second
combustion temperature lower than the first combustion temperature and
disposed in the first combustion chamber, and a first ignition unit for
directly igniting at least one of the first gas generating agent and the
second gas generating agent.

1. A gas generator comprising a housing having a gas discharge port,
ignition means for starting an operation of the gas generator and a gas
generating agent that generates gas by being ignited and burned in order
to inflate an air bag and at least one combustion chamber defined in the
housing, the gas generating agent being placed in at least one combustion
chamber, at least two types of gas generating agents having different
combustion temperatures from each other being placed in at least one of
the at least one combustion chamber.

2. A gas generator, comprising: a housing having a gas discharge port; a
first combustion chamber defined by the housing; a first gas generating
agent adapted to generate gas to inflate an air bag, the first gas
generating agent having a first combustion temperature and disposed in
the first combustion chamber; a second gas generating agent adapted to
generate gas to inflate the air bag, the second gas generating agent
having a second combustion temperature lower than the first combustion
temperature and disposed in the first combustion chamber; and first
ignition means for directly igniting at least one of the first gas
generating agent and the second gas generating agent.

3. The gas generator for an air bag as claimed in claim 2, wherein the
first gas generating agent is charged in an amount that enables the
second gas generating agent to be ignited and burned by combustion of the
first gas generating agent.

4. The gas generator for an air bag as claimed in claim 2, further
comprising: a partition member, having a communication hole, provided
inside the first combustion chamber for separating the first gas
generating agent and the second gas generating agent inside the first
combustion chamber.

5. The gas generator for an air bag as claimed in claim 4, wherein the
partitioning member partitions the interior of the first combustion
chamber in relation to the amount of first gas generating agent and the
second gas generating agent charged in the first combustion chamber.

6. The gas generator for an air bag as claimed in claim 3, further
comprising: a second combustion chamber defined within the housing; a
third combustion chamber defined within the housing; a third gas
generating agent adapted to generate gas to inflate the air bag, the
third gas generating agent having a third combustion temperature and
disposed in the second combustion chamber; a fourth gas generating agent
adapted to generate gas to inflate the air bag, the fourth gas generating
agent having a fourth combustion temperature lower than the third
combustion temperature and disposed in the second combustion chamber; and
second ignition means for directly igniting at least one of the third gas
generating agent and the fourth gas generating agent.

7. The gas generator for an air bag as claimed in claim 2 or 3, wherein
the first ignition means includes only an electric igniter ignited by
applying an operating current, and the first gas generating agent is
ignited directly by an activation of the electric igniter.

8. The gas generator for an air bag as claimed in claim 2 or 3, wherein
the first combustion temperature is between 1700 and 3000.degree. C., and
the second combustion temperature is between 1000 and 1700.degree. C.

9. The gas generator for an air bag as claimed in claim 6, wherein the
third combustion temperature is between 1700 and 3000.degree. C., and the
fourth combustion temperature is between 1000 and 1700.degree. C.

10. The gas generator for an air bag as claimed in claim 4, further
comprising: an inner cylinder provided inside the housing and extending
between a diffuser shell and a closure shell of the housing, wherein the
partition member is a part of the inner cylinder.

11. The gas generator for an air bag as claimed in claim 2, wherein the
first gas generating agent has a non-perforated shape and the second gas
generating agent has a single-perforated cylindrical shape.

12. The gas generator for an air bag as claimed in claim 1, including one,
two or three combustion chambers.

Description

RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. .sctn. 119(e) of
Provisional Application No. 60/537,541 filed on Jan. 21, 2004, and
incorporates by reference the subject matter of Application No. 2004-8356
filed in Japan on Jan. 15, 2004 on which a priority claim is based under
35 U.S.C. .sctn. 119(a).

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a gas generator for an air bag for
protecting a passenger from an impact of a collision.

[0004] 2. Description of Related Art

[0005] From the point of view of passenger protection, various demands
have been made in relation to a gas generator for an air bag which is
incorporated into an air bag system installed in an automobile. Examples
of these demands include ensuring that the gas generator can be operated
reliably over a typical expected lifespan (ten years or more) of the
vehicle in which the air bag system is installed.

[0006] To reduce the size of the gas generator, it is desirable that a gas
generating agent having a lower combustion temperature be used so that a
coolant filter can be simplified. Another desirable effect of using a gas
generating agent having a lower combustion temperature is that the amount
of gas components, such as NOx, generated during combustion of the gas
generating agent can be reduced.

[0007] However, it is also known that gas generating agents having a low
combustion temperature typically suffer from poor ignitability.
Nevertheless, to ensure that the gas generator operates reliably, it is
desirable that the gas generating agent possesses both good ignitability
and good combustibility.

[0008] Therefore, improving the cleanness of the gas and reducing the
weight of the gas generator are antithetical technologically to ensuring
operational reliability in terms of the ignitability and combustibility
of the gas generating agent.

[0009] Moreover, the output of the gas generator is modified according to
the type of vehicle to which the gas generator is installed. However,
modifying the container or components inside the container every time the
gas generator is installed leads not only to cost increases, but also to
errors in the component assembly.

[0010] In the gas generator disclosed in JP-A No. 11-334517, a transfer
charge is ignited and burned by an activation of an igniter, and a gas
generating agent is ignited and burned by the resulting flame. In the gas
generator disclosed in WO-A 01/72560, a transfer charge is ignited by the
ignition, through electrification of an igniter, and a gas generating
agent is burned by the resulting flame. Since the ignitability of a gas
generating agent comprising a nitrogen-containing organic compound is
particularly poor, an ignition chamber is provided to restrict the
outflow of gas in a circumferential direction.

[0011] JP-A No. 11-334517 makes no statement as to the combustion
temperature of the gas generating agent, and no references are made to
problems caused by the combustion temperature. With the constitution
disclosed in WO-A 01/72560, a gas generating agent having a lower
combustion temperature cannot be burned effectively. Moreover, since
there is no statement about using two or more types of gas generating
agent having different combustion temperatures, output cannot be adjusted
by combining gas generating agents having different combustion
temperatures.

SUMMARY OF THE INVENTION

[0012] The present invention provides a gas generator for an air bag which
can be reduced in weight while improving combustibility of a gas
generating agent during an operation so that operational reliability can
be ensured, and in which output adjustment can be performed easily while
ensuring that clean gas is generated and operational reliability is
sufficient.

[0013] The gas generator according to the present invention solves the
problems described above by using a gas generating agent having higher
combustion temperature and a gas generating agent having lower combustion
temperature in combination, such that the gas generating agent having the
lower combustion temperature is ignited and burned by the gas generating
agent having the higher combustion temperature.

[0014] More specifically, the present invention provides a gas generator
comprising a housing having a gas discharge port, ignition means for
starting an operation of the gas generator, and a gas generating agent
that generates gas by being ignited and burned in order to inflate an air
bag, wherein the gas generating agent is charged into at least one
combustion chamber defined in the housing, and at least two types of gas
generating agents having different combustion temperatures are charged
into at least one of the at least one combustion chamber.

[0015] In other words the invention is a gas generator comprising a
housing having a gas discharge port, ignition means for starting an
operation of the gas generator and a gas generating agent that generates
gas by being ignited and burned in order to inflate an air bag and at
least one combustion chamber defined in the housing, the gas generating
agent being placed in at least one combustion chamber, at least two types
of gas generating agents having different combustion temperatures from
each other being placed in at least one of the combustion chamber.

PREFERABLE EMBODIMENTS OF THE INVENTION

[0016] The invention includes preferably a gas generator, comprising:

[0017] a housing having a gas discharge port;

[0018] a first combustion chamber defined by the housing;

[0019] a first gas generating agent adapted to generate gas to inflate an
air bag, the first gas generating agent having a first combustion
temperature and disposed in the first combustion chamber;

[0020] a second gas generating agent adapted to generate gas to inflate
the air bag, the second gas generating agent having a second combustion
temperature lower than the first combustion temperature and disposed in
the first combustion chamber; and first ignition means for directly
igniting at least one of the first gas generating agent and the second
gas generating agent.

[0021] It is preferable that the first gas generating agent is charged in
an amount that enables the second gas generating agent to be ignited and
burned by combustion of the first gas generating agent.

[0022] It is preferable that the gas generator further comprising a
partition member, having a communication hole, provided inside the first
combustion chamber for separating the first gas generating agent and the
second gas generating agent inside the first combustion chamber.

[0023] It is preferable that the partitioning member partitions the
interior of the first combustion chamber in relation to the amount of
first gas generating agent and the second gas generating agent charged in
the first combustion chamber.

[0024] It is preferable that the gas generator further comprises:

[0025] a second combustion chamber defined within the housing;

[0026] a third combustion chamber defined within the housing;

[0027] a third gas generating agent adapted to generate gas to inflate the
air bag, the third gas generating agent having a third combustion
temperature and disposed in the second combustion chamber;

[0028] a fourth gas generating agent adapted to generate gas to inflate
the air bag, the fourth gas generating agent having a fourth combustion
temperature lower than the third combustion temperature and disposed in
the second combustion chamber; and

[0029] second ignition means for directly igniting at least one of the
third gas generating agent and the fourth gas generating agent.

[0030] It is preferable that the first ignition means includes only an
electric igniter ignited by applying an operating current, and the first
gas generating agent is ignited directly by an activation of the electric
igniter.

[0031] It is preferable that the first combustion temperature is between
1700 and 3000.degree. C., and the second combustion temperature is
between 1000 and 1700.degree. C.

[0032] It is preferable that the third combustion temperature is between
1700 and 3000.degree. C., and the fourth combustion temperature is
between 1000 and 1700.degree. C.

[0033] It is preferable that the gas generator further comprises an inner
cylinder provided inside the housing and extending between a diffuser
shell and a closure shell of the housing, wherein the partition member is
a part of the inner cylinder.

[0034] It is preferable that the first gas generating agent has a
non-perforated shape and the second gas generating agent has a
single-perforated cylindrical shape.

[0035] It is preferable that the gas generator includes one, two or three
combustion chambers.

DETAILED EXPLANATION OF THE INVENTION

[0036] With the gas generating agent described above, two or more types of
gas generating agent having different combustion temperatures are charged
into the same combustion chamber. The combustion temperature of the gas
generating agent may be determined using a logical calculation, for
example NEW PEP (new propellant evaluation program), which was created on
the basis of a basic program of the U.S. Naval Weapons Center. The
ignitability of a gas generating agent is typically commensurate with a
combustion temperature, and hence when a gas generator is operated, the
gas generating agent with the higher combustion temperature is preferably
ignited first, and the gas generating agent with the lower combustion
temperature is ignited and burned by the resulting flame. In so doing,
the combustion temperature within the combustion chamber is reduced below
that of a case in which only gas generating agents with a high combustion
temperature are used, in proportion to the amount of gas generating agent
with the lower combustion temperature that is used. As a result, a
coolant filter used to purify and cool the gas can be simplified (for
example, a coolant filter having sophisticated combustion gas
purification and combustion gas cooling effects is not required), and gas
components such as NOx can be reduced. Note that the charging amount of
the gas generating agent with the lower combustion temperature is
preferably greater than the charging amount of the gas generating agent
with the higher combustion temperature.

[0037] When the gas generator is operated, first, the gas generating agent
having the higher combustion temperature is ignited, and thus the gas
generating agent having the lower combustion temperature can be ignited
and burned reliably by the resulting flame. Using the gas generating
agent having the higher combustion temperature is particularly favorable
in that combustion continues for a long period of time (the gas
generating agent having the lower combustion temperature is exposed to a
high-temperature atmosphere for a long period of time), and hence the gas
generating agent having the lower combustion temperature can be burned
reliably by the resulting flame. Therefore, by combining these gas
generating agents, the operational reliability of the gas generator can
be ensured sufficiently, and hence an operationally reliable gas
generator can be provided while reducing the weight of the gas generator
and ensuring the cleanness of the generated gas. By varying the mixture
ratio of the gas generating agent having the higher combustion
temperature and the gas generating agent having the lower combustion
temperature when the two gas generating agents are mixed, the combustion
temperature of the gas generating agents used in the gas generator as a
whole can be adjusted. Accordingly, by adjusting the charging ratio of
the two gas generating agents, the output of the gas generator can be
finely controlled, and hence there is no need to modify the
constitutional components of the gas generator in order to achieve the
required output. As a result, component assembly errors occurring when
the constitutional components are modified can be eliminated.

[0038] Note, however, that in order to obtain these effects in the present
invention, the two or more types of gas generating agents that are
charged into the same combustion chamber should have different combustion
temperatures. By using a combination of gas generating agents having
different combustion temperatures, the gas generator of the present
invention achieves effective combustion of the gas generating agent with
the lower combustion temperature, a decrease in the combustion
temperature of the gas generating agent as a whole, an improvement in the
cleanness of the gas and a reduction in the weight of the gas generator.

[0039] In the gas generator of the present invention, the form and
dimensions of the gas generating agents may be the same or different for
the gas generating agent having the lower combustion temperature and the
gas generating agent having the higher combustion temperature that are
disposed in the same combustion chamber.

[0040] Further, the gas generating agent generates gas for inflating an
air bag and simultaneously generates heat through combustion, but the
heat is absorbed not only by the generated gas, but also by solid
residue, and hence a gas generating agent which generates a large amount
of heat does not necessarily have a high combustion temperature. It is
therefore difficult to adjust the output according to the ratio of gas
generating agents which generate different amounts of heat. In the gas
generator of the present invention, on the other hand, at least two types
of gas generating agents having different combustion temperatures are
used, and these gas generating agents are disposed in the same combustion
chamber. Thus, the combustion temperatures of the gas generating agents
can be adjusted reliably. The gas generator of the present invention may
be a single type comprising single ignition means or a dual type
comprising two ignition means. Alternatively, the gas generator may be a
multi-type gas generator comprising three or more ignition means.

[0041] It is preferable in the present invention that a gas generating
agent having the higher combustion temperature, among the at least two
types of gas generating agents disposed in the same combustion chamber,
is charged in an amount enabling a gas generating agent with the lower
combustion temperature to be ignited and burned, and such that the
charging amount thereof can be adjusted optionally.

[0042] In the gas generator of the present invention, the gas generating
agent having the higher combustion temperature, among the at least two
types of gas generating agent disposed in the same combustion chamber,
may be used in an amount at which the gas generating agent having the
lower combustion temperature can be ignited and burned. The usage amount
of the gas generating agent having the higher combustion temperature may
be determined according to the composition, compositional ratio, form,
and size of the respective gas generating agents, the usage amount of the
gas generating agent having the lower combustion temperature, and so on.

[0043] The required output of the gas generator during an operation may
differ depending on the vehicle type to which the gas generator is
installed. If the internal constitution (or the constitutional
components) is modified for every required output, assembly errors become
more likely to occur. Output modification is performed typically by
modifying the charging amount of the gas generating agent, or changing a
cooling agent such as the filter or the coolant.

[0044] In the present invention, the gas generating agents having
different combustion temperatures that are charged in the same combustion
chamber are preferably charged in the amounts that can be adjusted
optionally. The charging amount of each gas generating agent can be
adjusted by adjusting the usage amounts of the respective gas generating
agents charged into the same combustion chamber, the combined usage
amount of the gas generating agents charged into the same combustion
chamber, and the usage proportions of the gas generating agent having the
higher combustion temperature and the gas generating agent having the
lower combustion temperature which are charged into the same combustion
chamber. For example, the charging amounts may be determined taking into
consideration not only the ignitability of the gas generating agent
having the lower combustion temperature, but also the combustion
temperature generated in the combustion chamber. By combining gas
generating agents with different combustion temperatures and adjusting
the proportions and so on thereof, the temperature of the gas generated
by the combined gas generating agent can be varied, thus enabling fine
adjustment of the output. In other words, by varying the mixing ratio of
the gas generating agents with different combustion temperatures, the
temperature of the gas generated from the combined gas generating agent
can be adjusted, thus enabling adjustment of the output of the gas
generator. Particularly when the ratio of the gas generating agent having
the higher combustion temperature and the gas generating agent having the
lower combustion temperature charged into the same combustion chamber is
varied, the volume of the entire combustion chamber does not change, and
hence superfluous gaps and the like do not occur in the combustion
chamber. The gas generating agents that can be charged into the same
combustion chamber will be described in detail in the following
embodiments.

[0045] It is preferable in the present invention that the ignition means
comprises only an electric igniter activated by an operating current, and
the gas generating agent having the higher combustion temperature, among
the at least two types of gas generating agent, is adapted to be ignited
directly by an activation of the electric igniter.

[0046] Instead of charging gas generating agents having different
combustion temperatures into the same combustion chamber in an evenly
mixed state, the charging amount of at least one of the types of gas
generating agent may be distributed unevenly within the combustion
chamber. When the charging amount of one of the gas generating agents is
distributed unevenly, the gas generating agent having the higher
combustion temperature, among the two or more types of gas generating
agent, is preferably positioned, such that it may be ignited directly by
the ignition means (electric igniter or the like). In most cases, the
phrase "positioned such that it may be ignited directly by the ignition
means (electric igniter or the like)" indicates it is provided in the
vicinity of the ignition means, but when the flame and so on of the
ignition means are guided to another location by a member (such as a tube
or the like) or by the constitution of the gas generator, this phrase
indicates the position to which the flame and so on of the ignition means
are guided by the member. Specifically, the phrase "the vicinity of the
ignition means" signifies that the gas generating agent having the higher
combustion temperature is in contact with the ignition means, or if not
in contact, at least within a range where it can be ignited by the
ignition means before the gas generating agent having the lower
combustion temperature.

[0047] By positioning the gas generating agent having the higher
combustion temperature adapted to be ignited directly by the ignition
means (such as electric igniter or the like) in this manner, the gas
generating agent can be ignited and burned quickly and reliably, and
hence all of the gas generating agents can be ignited and burned quickly
and reliably. As a result, the operational reliability of the gas
generator can be improved. In other words, since the gas generating agent
having the higher combustion temperature typically has good ignitability,
the gas generating agent having the higher combustion temperature can be
ignited and burned directly by the ignition means alone. Therefore, when
the gas generating agents having different combustion temperatures are
used, the gas generating agent having the higher combustion temperature
is disposed closer to the igniter (e.g., in contact therewith or at a
distance enabling ignition) so that the gas generating agent having the
high combustion temperature can be ignited and burned quickly and
reliably, and so that the ignitability and combustibility of the gas
generating agent having the lower combustion temperature can be improved
by the resulting flame. Hence when the gas generating agents charged into
the same combustion chamber are divided into a plurality of layers
according to the combustion temperature of the gas generating agent, the
ignition means, the gas generating agent having the higher combustion
temperature, and the gas generating agent having the lower combustion
temperature are preferably arranged or ignited in that order.

[0048] Note that the ignition means may include a transfer charge and an
electric igniter. In this case, the transfer charge is ignited by
activation of the igniter, and the transfer charge produces ignition
energy in the form of a flame, high-temperature gas, and so on. This
ignition energy ignites and burns the gas generating agent having the
higher combustion temperature, and the resulting combustion energy
ignites and burns the gas generating agent having the lower combustion
temperature. The transfer charge used in the ignition means amplifies the
thermal energy generated by activation of the igniter. Therefore, the gas
generating agent is burned effectively, and thus differs from the gas
generating agent having the higher combustion temperature in that it is
not used to substantially generate a gas which contributes to inflation
of the air bag. Accordingly, in the present invention, the transfer
charge may be seen as an object having a gas generation efficiency of
less than 1.2 mol/100 g. A mixture of boron and potassium nitrate (nitre)
is used typically as this transfer charge. However, to reduce the size
and weight of the gas generator, the ignition means is preferably
constituted only by an electric igniter, and the gas generating agent
having the higher combustion temperature is preferably ignited and burned
directly by the electric igniter alone.

[0049] Further, this type of conventional transfer charge can be
distinguished clearly from the gas generating agent having the higher
combustion temperature used in the present invention in that since the
transfer charge is used in a powder form, it burns instantaneously,
producing only a minute amount of gas, and therefore cannot be used to
inflate the air bag. Moreover, combustion of the transfer charge mainly
produces thermal residue, and hence the transfer charge cannot be used
for fine control of the output of the gas generator.

[0050] It is preferable in the present invention that at least two types
of gas generating agents disposed in the same combustion chamber are
partitioned and charged separately from each other according to the type
within the same combustion chamber by a partitioning member(s) having a
communicating hole.

[0051] When the gas generating agents charged in the same combustion
chamber are divided into a plurality of layers according to the
combustion temperature of the gas generating agent, the at least two
types of gas generating agents disposed in the same combustion chamber
are preferably partitioned separately from each other according to type
within the same combustion chamber by a partitioning member(s) having a
communicating hole. By partitioning a single combustion chamber using the
partitioning member, the gas generating agents can be charged easily, and
mixing of the gas generating agents caused by vibration when the gas
generator is loaded into a vehicle can be prevented. In other words, when
the partitioning member is used, the gas generating agent having the
lower combustion temperature can be held in a desired location (e.g., in
the vicinity of the ignition means or the like) securely.

[0052] When one or all of the combustion chambers are partitioned using a
partition plate, partitioning may be performed using an appropriate
cushioning member formed to communicate the partitioned spaces with each
other by becoming displaced, shifting, rupturing, vanishing, or a similar
action caused by combustion of the gas generating agent, instead of a
partition plate comprising the aforementioned communicating hole. This
cushioning member may be formed into a flat plate form which matches the
cross-sectional form of the combustion chamber in which it is disposed,
or an appropriate three-dimensional form which can be disposed inside the
combustion chamber, using an appropriate material such as a resin
material, for example. Needless to say, the cushioning member may also be
formed with a communicating hole for communicating the partitioned spaces
with each other. Further, instead of a communicating hole, the
partitioning member or cushioning member may be formed in a dimension
which allows the formation of a gap with the member which partitions the
combustion chamber, and this gap (for example, a gap between the inner
peripheral wall of the combustion chamber and the edge portion of the
partitioning member) may be used in place of the communicating hole.

[0053] The partitioning member is preferably disposed to partition the
interior of the combustion chamber in which the partitioning member is
disposed in accordance with the amount of each gas generating agent
charged in the combustion chamber. In other words, it is desirable that
the gas generating agent having the higher combustion temperature and the
gas generating agent having the lower combustion temperature can be
adjusted optionally in accordance with their respective ignitability,
usage amounts, usage proportion, and so on. If it is possible at this
time to adjust the volume of the space into which each gas generating
agent is to be charged, the gas generating agents can be charged
appropriately while preventing mixing of and damage to the gas generating
agents caused by vibration when the gas generator is loaded into the
vehicle. The partitioning member may be fixed inside the combustion
chamber by being inserted therein with force, for example, so that the
interior of the combustion chamber can be partitioned freely in
accordance with the charging amount of each gas generating agent.

[0054] A communicating hole is formed in the partitioning member to
communicate the partitioned space with each other. The communicating hole
may be formed not to influence the combustion performance of the gas
generating agent, or the opening area of the communicating hole (e.g.,
the total opening area when a plurality of communicating holes are
provided) may be associated with the surface area of the gas generating
agent so that by adjusting the combustion performance of the gas
generating agent disposed in the space on the upstream side of the
partitioning member (e.g., the side that is furthest from the gas
discharge holes), the internal combustion pressure in the space is
adjusted. Further, the communicating hole may be closed by an aluminum
tape or the like having a thickness of approximately 50 to 100 .mu.m
(i.e., the combined thickness of the adhesive layer and the base portion)
which is ruptured by the pressure generated during combustion, or may be
covered with a silicon cushion or the like which is burned by the heat
generated during combustion.

[0055] It is preferable in the present invention that at least one
combustion chamber is separated inside the housing according to the
ignition means for igniting and burning the gas generating agent charged
therein, and at least one type of gas generating agent charged in one of
the at least one combustion chamber is ignited and burned by ignition
means.

[0056] Although the single combustion chamber is partitioned by the
partitioning member as described above, the communicating hole is formed
in the partitioning member, and, therefore, the spaces in which the
different gas generating agents are accommodated may communicate with
each other. Furthermore, combustion of the gas generating agents is
initiated by the activation of a single igniter, and hence the spaces
partitioned by the partitioning member are not individual combustion
chambers, but form a single combustion chamber in combination. Therefore,
in the present invention, the at least one "combustion chamber" separated
in the housing are separated according to the ignition means for igniting
and burning the gas generating agents charged therein, and the at least
one gas generating agent charged in the at least one combustion chamber
is ignited and burned successively by one of the ignition means. Hence,
even when the partitioning member is provided in the combustion chamber
so that the spaces accommodating the different gas generating agents are
partitioned thereby, the gas generating agents are perceived to be
disposed together in a single combustion chamber as long as they are
burned in succession by the activation of a single igniter. This holds
not only for a single-type gas generator, but also for a dual-type gas
generator in which two sets of a combustion chamber and a corresponding
ignition means are provided, and a multi-type gas generator in which
three or more sets are provided.

[0057] Particularly, when the gas generator is a dual or multi-type, the
two or more types of gas generating agents having different combustion
temperatures may be disposed together (e.g., mixed) in all of the
combustion chambers provided in the gas generator, or may be disposed
together (e.g., mixed) in only one of the combustion chambers.

[0058] In the gas generator of the present invention, to ensure that the
gas generating agent as a whole is sufficiently ignitable while
suppressing the combustion temperature thereof to a low level, the
combustion temperature of the gas generating agent having the highest
combustion temperature, among the at least two types of gas generating
agents having different combustion temperatures, is preferably between
1700 and 3000.degree. C., and the combustion temperature of the gas
generating agent having the lowest combustion temperature is preferably
between 1000 and 1700.degree. C. Moreover, the gas generating agent
having the highest combustion temperature, among the two or more types of
gas generating agent charged in the same combustion chamber, preferably
generates gas of no less than 1.2 mol/100 g.

[0059] When the gas generating agent having the higher combustion
temperature and the gas generating agent having the lower combustion
temperature are disposed in a single combustion chamber and partitioned
by the partitioning member, the gas generating agent having the lower
combustion temperature is preferably set at a greater charging ratio. In
so doing, the temperature of the gas generated from the gas generating
agent as a whole is reduced, enabling reductions in the amount of
coolant, and the weight and size of the gas generator. Although the gas
generating agents charged in the same combustion chamber have different
combustion temperatures, they are still both gas generating agents, and
hence the gas generated by the gas generating agent ignited and burned
directly by the electric igniter can also be used to inflate the air bag.
As a result, the charging amount of the gas generating agent for
inflating the air bag can also be reduced.

[0060] In the gas generator of the present invention, when a gas
generating agent which generates ammonia through combustion is used as
the gas generating agent having the higher combustion temperature and a
gas generating agent which generates NOx through combustion is used as
the gas generating agent having the lower combustion temperature, the
respective gases can be converted into nitrogen gas by a reaction of the
generated NOx and ammonia. As a result, the amount of NOx discharge can
be reduced reliably, and the amount of ammonia discharge can also be
reduced.

[0061] According to the gas generator of the present invention as
described above, the combustion temperature of the gas generating agent
in the entire gas generator can be reduced, and hence the coolant filter
can be simplified, enabling a reduction in the size of the gas generator.
Moreover, since the combustion temperature of the gas generating agent is
suppressed to a low level, gas components such as NOx generated during
combustion of the gas generating agent can be reduced. In the gas
generator of the present invention, the ignitability and combustibility
of the gas generating agent can be ensured even though the combustion
temperature of the gas generating agent is reduced in this manner, or in
other words, even when a gas generating agent that typically has poor
ignitability is used, and hence the operational reliability of the gas
generator can be ensured. In short, according to the present invention,
conventional antithetical technological problems relating to the
ignitability and combustibility of a gas generating agent can be solved.

[0062] Furthermore, in the gas generator of the present invention, by
adjusting the overall charging amount of the gas generating agents having
different combustion temperatures that are charged in the same combustion
chamber, or the charging proportions thereof, the output of the gas
generator can be adjusted easily.

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The present invention will become more fully understood from the
detailed description given herein below and the accompanying drawings
which are given by way of illustrations only, and thus are not limitative
of the present invention, and wherein:

[0064] FIG. 1 is an axial sectional view of a gas generator for an air
bag.

[0065] An embodiment of the present invention will be described below with
reference to the drawing. FIG. 1 is an axial sectional view of a gas
generator for an air bag of the present embodiment. Note that in the
following description, the longitudinal relationship between the terms
"upper" and "lower" is based on FIG. 1. Moreover, the axial direction
denotes the axial direction of the housing, and the radial direction
denotes the radial direction of the housing.

[0066] An outer shell container of a gas generator 10 has a housing 11
formed by joining a diffuser shell 12 and a closure shell 13 which
defines an internal storage space together with the diffuser shell 12.
The diffuser shell 12 and the closure shell 13 are welded at a welding
portion 14. The black-shaded parts of FIG. 1 indicate other welding
portions.

[0067] Gas discharge ports 17, 18 are provided along the circumferential
direction of the diffuser shell 12 in a required number, and these gas
discharge ports 17, 18 are closed by an aluminum seal tape 75. The gas
discharge ports 17 and gas discharge ports 18, arranged in series along
the circumferential direction and may have the same or a different
diameter.

[0068] An inner cylinder 15 having a substantially cylindrical shape is
disposed inside the housing 11. The upper peripheral edge of the inner
cylinder 15 is joined to a ceiling surface 12a of the diffuser shell 12,
and the lower peripheral edge thereof is joined to a base surface 13a of
the closure shell 13. As a result, a space isolated from the outside
environment is formed inside the housing. At the outside of the inner
cylinder 15, and a space (i.e., a part of a first combustion chamber) for
accommodating a first gas generating agent 20b, described below, is
provided. A single collar 33, to which a first igniter 31 and a second
igniter 32 are fixed, is provided in the lower side opening of the inner
cylinder 15, thereby closing the interior of the inner cylinder 15. Note
that in cases where an air bag module including the gas generator 10 is
installed in a vehicle, the first igniter 31 and the second igniter 32
are connected to a device (and a power source) for controlling operations
of the gas generator via a connector, lead wires, and so on.

[0069] A partition wall 40 is provided in the inner cylinder 15 for
dividing the space in the interior of the inner cylinder 15 into upper
and lower sections. The partition wall 40 has a flat circular shape
comprising a skirt portion 41, which surrounds the periphery of the
second igniter 32, and a second through hole 52 formed in a part
surrounded by the skirt portion. The partition wall is fitted into a
stepped notch portion 16 of the inner cylinder 15 from the lower side.
Since the partition wall 40 engages the stepped notch portion 16 of the
inner cylinder 15 as described above, it is prevented from moving upward
by the pressure generated even when the first igniter 31 is activated.
Moreover, since the inner diameter of the skirt portion 41 is set to be
substantially identical to the outer diameter of the ignition part of the
igniter 32 such that the skirt portion 41 surrounds the ignition part in
an airtight fashion, the flame generated by an activation of the second
igniter 32 advances only in the direction of the second through hole 52.

[0070] The first igniter 31 and a first gas generating agent 20a charged
in an aluminum cup 35 are disposed in a space outside of the skirt
portion 41 (i.e., the space separated by the skirt portion 41 from the
space in which the second igniter 32 exists) in the lower space inside
the inner cylinder 15 partitioned by the partition wall 40 (i.e., the
space closed by the collar 33). Hence in the gas generator according to
this embodiment, the first gas generating agent 20a, which is disposed in
the same space as the first igniter 31, and the first gas generating
agent 20b, which is disposed in the separated space on the outside of the
inner cylinder 15 in the radial direction, are used as first gas
generating agents.

[0071] The two first gas generating agents 20a, 20b have different
combustion temperatures. The first gas generating agent 20a, disposed in
the same space as the first igniter 31 has a higher a high combustion
temperature, and the first gas generating agent 20b disposed in the
separated space outside the inner cylinder 15 in the radial direction has
a lower combustion temperature. Further, the first gas generating agent
20a having a higher combustion temperature is non-perforated, and its
dimensions (e.g., diameter, length) per particle are smaller than those
of the first gas generating agent 20b having a lower combustion
temperature, whereas the first gas generating agent 20b having a lower
combustion temperature has a single-perforated cylindrical form. Note,
however, that there are no particular limitations as to the form of the
first and second gas generating agents that may be used in the gas
generator, and a disk-form having a through hole or a hollow (e.g.,
having a recessed portion), a columnar form having a through hole or a
hollow (e.g., having a recessed portion), and so on may be employed.
Moreover, the gas generating agent having the higher combustion
temperature may take the same form as the gas generating agent having the
lower combustion temperature.

[0072] The space outside the inner cylinder 15 in the redial direction, in
which the first gas generating agent 20b having a lower combustion
temperature is accommodated, and the space accommodating the first gas
generating agent 20a having a higher combustion temperature, in which the
first igniter 31 is disposed, are connected by a first through hole 51.
Since the gas generating agents 20a and 20b in these two spaces are
ignited and burned successively by an activation of the first igniter 31,
the two combined spaces serves as a single combustion chamber (i.e., a
first combustion chamber 20). Thus the first gas generating agents 20a
and 20b having different combustion temperatures are charged in the same
combustion chamber (i.e., the first combustion chamber 20).

[0073] By disposing the partition wall 40 having the skirt portion 41 in
the inner cylinder 15, a second combustion chamber 25 is separated from
the two igniters, and the first igniter 31 is separated from the second
igniter 32. As a result, the ignition energy (e.g., a flame, combustion
gas, and so on) generated by an activation of the first igniter 31 flows
exclusively into the first combustion chamber, is prevented from
infiltrating the second ignition means chamber, and passes through the
second through hole 52 into the second combustion chamber 25.

[0074] The gas generating agent 20a charged in an aluminum cup 35 is
positioned directly above the first igniter 31, and the first through
hole 51 provided in a lower portion of a side wall of the inner cylinder
15 is positioned substantially directly opposing the center of the
aluminum cup 35. This position does not directly face the direction of
advancement of the flame generated by an activation of the first igniter
31. Note that aluminum or stainless steel seal tape 60 is adhered to the
first through hole 51 from the inside.

[0075] By disposing the first through hole 51 and the aluminum cup 35,
accommodating the gas generating agent 20a, face one another directly in
this manner, all of the gas generating agent 20a is burned substantially
evenly by an activation of the first igniter 31.

[0076] Further, the first through hole 51 is provided in the lower portion
of the inner cylinder 15, and a shielding plate 66 is provided at a
position directly facing the first through hole 51 in the space in which
the first gas generating agent 20b is provided and inside a cylindrical
filter 65 provided facing the peripheral wall surface of the housing. The
shielding plate 66 of this embodiment has a tube portion 92 and an
outward flange-shaped circular portion 93 formed integrally with and
extending from one side (i.e., the lower side in FIG. 1) of the tube
portion 92. The shielding plate 66 is formed such that the circular
portion 93 contacts the base surface 13a and the tube portion 92 covers a
predetermined range of the lower portion of the cylindrical filter 65
(e.g., a height range of approximately {fraction (1/2)} to 2/3 of the
entire height of the cylindrical filter 65).

[0077] By providing this shielding plate 66, the high-temperature gas and
flame generated by combustion of the first gas generating agent 20a
(e.g., the energy generated by combustion of the gas generating agent
20a) are ejected through the first through hole 51 and collide with the
shielding plate 66 (the tube portion 92 in particular) such that the
advancement direction of the energy is changed from the radial direction
to an upward axial direction. The energy thus advances toward the space
in which the first gas generating agent 20b is provided. As a result, the
overall ignitability of the first gas generating agent 20b is improved.
It is therefore preferable that the axial length of the shielding plate
66 be extended upward at least beyond the first through hole 51. Note
that the same actions and effects as those illustrated in FIG. 1 can be
obtained by providing a shielding plate so as to cover the entire inner
peripheral surface of the filter 65 and forming a plurality of gas vents
in part thereof. Moreover, a shielding plate (not shown) similar to the
shielding plate 66, comprising the tube portion 92 and a circular portion
formed integrally with and extending from one side (i.e., the lower side
in FIG. 1) of the tube portion 92 to cover the outer periphery of the
filter 65, may be provided on the outside of the filter 65.

[0078] The shielding plate 66 may be positioned in relation to the housing
by bringing the outer peripheral edge portion of the circular portion 93
into contact with a curved portion 94 of the housing. Filter positioning
during assembly may be performed by bringing the inner peripheral surface
of the filter 65 into contact with the lower-side outer peripheral
surface of the tube portion 92. The tube portion 92 is formed and
disposed to secure an annular gap 71 between the tube portion 92 and the
inner peripheral surface of the filter 65. In so doing, combustion gas
(in other words, gas for inflating the air bag generated by combustion of
the gas generating agent) also enters the gap 71, enabling an improvement
in the filtering efficiency and cooling efficiency.

[0079] By means of the structure or configuration at the side of the first
combustion chamber 20 provided in the housing 11 as described above, all
of the first gas generating agent 20a having a higher combustion
temperature that is charged into the aluminum cup 35 burns quickly and
evenly when the first igniter 31 is activated. The resulting flame
ruptures the seal tape 60 to flow through the first through hole 51 in
the lower portion of the side wall of the inner cylinder 15 into the
space on the outside of the inner cylinder 15 of the same first
combustion chamber, in which the first gas generating agent 20b having a
lower combustion temperature is charged. The flame is then directed
throughout the entire space by the shielding plate 66 so that the first
gas generating agent 20b having a lower combustion temperature is ignited
and burned. The first gas generating agent 20b having a lower combustion
temperature typically has poor ignitability, but since the first gas
generating agent 20a having favorable ignitability burns sufficiently and
over a long period of time, even the first gas generating agent 20b
having a lower combustion temperature can be ignited and burned quickly
and reliably. Moreover, the combustion heat generated in the first
combustion chamber from the first gas generating agent as a whole is
reduced in accordance with the amount of the first gas generating agent
20b having a lower combustion temperature that is used.

[0080] The space above the partition wall 40 insider the inner cylinder 15
is formed as the second combustion chamber 25, and a second gas
generating agent 25a and a second gas generating agent 25b having
different combustion temperatures are accommodated in the second
combustion chamber 25. In this embodiment, the second gas generating
agent 25a having a higher combustion temperature is charged on the side
of the second combustion chamber 25 in which the partition wall 40 is
provided (i.e., the lower side), and the second gas generating agent 25b
having a lower combustion temperature is charged above the partition wall
40. The two types of second gas generating agents 25a and 25b having
different combustion temperatures are charged in the same second
combustion chamber 25, and are partitioned according to type by a
partitioning member, or in other words a partition plate 96, having a
communicating hole 95. The communicating hole 95 may be closed by a seal
tape, not shown in the drawing. The partition plate 96 is inserted
forcibly into the inner cylinder 15 from below, and the seal tape 60 is
preferably adhered to the partition plate 96 after insertion of the
partition plate so that the tape does not rupture during the insertion.

[0081] The space accommodating the second gas generating agent 25a having
a higher combustion temperature and the space accommodating the second
gas generating agent 25b having a lower combustion temperature are
connected by the communicating hole 95, and since the gas generating
agents provided in these two spaces are ignited and burned successively
by an activation of the second igniter 32, the two combined spaces form a
single combustion chamber (i.e., the second combustion chamber 25).
Therefore, the second gas generating agents 25a and 25b having different
combustion temperatures are charged inside the same combustion chamber
(i.e., the second combustion chamber 25).

[0082] Particularly in this embodiment, the second gas generating agent is
similar to the first gas generating agent in that the second gas
generating agent 25a having a higher combustion temperature is
non-perforated, and its dimensions (e.g., diameter, length) per particle
are smaller than those of the second gas generating agent 25b having a
lower combustion temperature, whereas the second gas generating agent 25b
having a lower combustion temperature has a single-perforated cylindrical
form. The two gas generating agents are disposed to be ignited (or
inflamed) by the igniter 32 in order of the second gas generating agent
25a and then the second gas generating agent 25b.

[0083] The partition plate 96 is inserted forcibly into the second
combustion chamber 25 such that the disposal location thereof can be
adjusted optionally. Accordingly, the second gas generating agents 25a,
25b can be charged at an arbitrary mixture ratio. In this embodiment, the
charging amount of the gas generating agent 25b having a lower combustion
temperature is greater than that of the gas generating agent 25a having a
higher combustion temperature, and hence the overall combustion
temperature of the second combustion chamber 25 is suppressed to a low
level.

[0084] Further, since the disposal location of the partition plate 96 can
be adjusted optionally, the charging ratio of the second gas generating
agents 25a, 25b having different combustion temperatures can also be
adjusted optionally. Accordingly, the temperature of the gas generated
from the second combustion chamber can be adjusted as desired, enabling
the output of the gas generator to be adjusted. By increasing the
charging amount of the gas generating agent having a lower combustion
temperature, the overall temperature of the gas generated from the second
combustion chamber decreases, enabling a reduction in an amount of the
filter 65. As a result, the overall size and weight of the gas generator
can be reduced.

[0085] Further, the second gas generating agent 25b has a lower combustion
temperature than the second gas generating agent 25a, and therefore
typically exhibits poor ignitability. In the gas generator shown in FIG.
1, however, the second gas generating agent 25a having a higher
combustion temperature is ignited and burned first by the second igniter
32, and thus sufficient ignition energy is supplied to the second gas
generating agent 25b having a lower combustion temperature. As a result,
the combustibility of the second gas generating agent accommodated inside
the second combustion chamber 25 is improved.

[0086] Since boron nitre (B/KNO.sub.3), which is used conventionally as a
transfer charge, is employed in a powder form and burns out
instantaneously, it is difficult to supply the second gas generating
agent 25b having a lower combustion temperature with sufficient ignition
energy. In the gas generator according to the present invention, however,
the second gas generating agent 25b can be supplied with sufficient
ignition energy for a comparatively long period of time through
combustion of the second gas generating agent 25a having a higher
combustion temperature, which is extremely beneficial in ensuring that
the second gas generating agent 25b is ignited and burned reliably. Use
of the second gas generating agent 25a is also beneficial in that gas for
inflating the air bag can also be supplied.

[0087] Note that in this embodiment, the gas generating agents 25a, 25b
are separated by the partition plate 96. However, the gas generating
agents 25a, 25b may be mixed evenly and disposed in the second combustion
chamber without using the partition plate 96, or the gas generating
agents 25a, 25b may be localized as shown in FIG. 1, without using the
partition plate 96. Note, however, that the partition plate 96 formed
with the communicating hole 95 is preferably used to adjust the
combustion performance of the gas generating agents 25a, 25b. The reason
for this is that by adjusting the overall opening area of the
communicating hole 95 in relation to the entire surface area of the gas
generating agent 25a, the combustion performance of the gas generating
agent 25a can be adjusted. Meanwhile, by adjusting the total opening area
of a communicating hole 80, that communicates the first combustion
chamber 20 with the second combustion chamber, in relation to the overall
surface area of the gas generating agent 25b, the combustion performance
of the gas generating agent 25b can be adjusted. Note that when the gas
generating agent does not require combustion performance adjustment
according to the characteristics thereof, then naturally there is no need
to adjust the combustion performance of the gas generating agent using
the communicating holes in the partition plate. In this case, the two
types of gas generating agents can be distributed unevenly or mixed by
increasing the size of the communicating holes or removing the partition
plate itself.

[0088] A cylindrical retainer 55 having a bottom is fitted into the second
combustion chamber 25 with the opening portion side thereof facing
downward, and fixed to the second combustion chamber 25 by being pressed
against an inner wall 25c thereof at a side wall tip end portion 55a. The
retainer 55 may be formed with a plurality of openings (e.g., nozzles) in
its side wall portions, or the entire retainer 55 may be formed of a
porous material such as wire mesh, so that it has substantially no
pressure loss. The retainer 55 is disposed to form a gap 57 large enough
to secure a gas passage between its side wall and the inner wall 25c of
the second combustion chamber 25.

[0089] As a result, the gas generating agent 25b does not make contact
with the communicating hole 80, and hence the communicating hole 80 is
not blocked by the unburned gas generating agent 25b in the vicinity of
the communicating hole 80. If the communicating hole 80 were blocked by
the second gas generating agent, the internal pressure of the second
combustion chamber 25 would rise excessively during the initial stage of
combustion, and when the second gas generating agent blocking the
communicating hole 80 was burned, the internal pressure would drop
dramatically as the communicating hole 80 opened, leading to a possible
reduction in the combustion stability. In the gas generator of this
embodiment, however, the communicating hole 80 is not blocked by the
unburned gas generating agent 25b, and hence such a problem can be
eliminated. A similar member may be employed to form a gap between the
gas generating agent 25a and the communicating hole 95 formed in the
partition plate 96.

[0090] The communicating hole 80 is closed by a stainless steel seal tape
58 from the outside. Characteristics such as the material, thickness, and
closing constitution or configuration of this seal tape are selected such
that the communicating hole 80 is opened only when the second gas
generating agents 25a and 25b are burned, and not when the first gas
generating agents 20a and 20b are burned.

[0091] Note that the charging ratio of the gas generating agents 20b, 20a
having different burning rates in the first combustion chamber 20 can
also be adjusted. To illustrate an example of such an aspect on the basis
of FIG. 1, a retainer 98 for retaining the gas generating agent 20b
having a lower combustion temperature is disposed near the center of the
housing axial direction, for example, whereupon the gas generating agent
20b having a lower combustion temperature and the gas generating agent
20a having a higher combustion temperature are disposed at the diffuser
12 side and the closure 13 side, respectively. At this time, the first
gas generating agent 20a having a higher combustion temperature is also
disposed in a space 90 of the first combustion chamber in which the
second igniter is accommodated. By forming the retainer 98 so that it can
be inserted forcibly, the charging ratio of the two first gas generating
agents can be adjusted optionally. However, as mentioned in the
description relating to the second combustion chamber, the charging
amount of the gas generating agent having a lower combustion temperature
is preferably increased in the first combustion chamber so that the
weight of the coolant and the size of the gas generator can be reduced.

[0092] In a dual type gas generator in which two combustion chambers are
provided within a housing, as in the gas generator described above with
reference to FIG. 1, adjustment of the charging ratio of the two types of
gas generating agents that are charged into the same combustion chamber
may be performed in either of the first combustion chamber or second
combustion chamber, or in both combustion chambers.

[0093] In the gas generator according to this embodiment, a gas generating
agent having a combustion temperature of 1700 to 3000.degree. C., for
example, may be used as the gas generating agents 20a, 25a having a
higher combustion temperature, disposed in the first combustion chamber
and second combustion chamber, respectively. An example of such a gas
generating agent is a gas generating agent having nitroguanidine as a
fuel and strontium nitrate as an oxidizer. Where necessary, a binder
(e.g., sodium carboxymethylcellulose) and a residue collecting agent
(e.g., Japanese acid clay) may be used.

[0094] The following composition, for example, may be used for the first
and second gas generating agents having a higher combustion temperature:

[0095] (a) nitroguanidine of approximately 25 to 55% by mass, or
preferably 30 to 40% by mass;

[0096] (b) strontium nitrate of approximately 40 to 65% by mass, or
preferably 45 to 65% by mass;

[0097] (c) Japanese acid clay of approximately 1 to 20% by mass, or
preferably 3 to 7% by mass; and

[0098] (d) a binder of approximately 3 to 12% by mass, or preferably 4 to
12% by mass.

[0099] The first and second gas generating agents having a higher
combustion temperature are formed in a pellet form with an outer diameter
of 0.8 to 4.0 mm and a length of 0.8 to 4.0 mm, or may be formed in a
single-perforated cylindrical form having an outer diameter of 1.2 to 6.0
mm and a length of 0.8 to 6.0 mm, and a through hole with an inner
diameter of 0.5 to 2.0 mm.

[0100] Further, a gas generating agent disclosed in JP-B No. 3247929 may
be used as the first and second gas generating agents having a higher
combustion temperature. The gas generating agents shown in the following
Table 1, for example, are included as this gas generating agent.

[0101] Meanwhile, a gas generating agent having a combustion temperature
of 1000 to 1700.degree. C., for example, may be used as the gas
generating agents 20b, 25b having a lower combustion temperature,
disposed in the first combustion chamber and second combustion chamber,
respectively. An example of such a gas generating agent is a gas
generating agent having guanidine nitrate as a fuel and a basic copper
oxide as an oxidizer. Where necessary, the aforementioned binder and
residue collecting agent, or a substance containing a coolant (e.g.,
aluminum hydroxide), may be used.

[0102] A composition containing the following components (a) to (c), for
example, may be used for the first and second gas generating agents
having a lower combustion temperature:

[0103] (a) an organic compound serving as a fuel of preferably 5 to 60% by
mass, more preferably 10 to 60% by mass, and even more preferably 10 to
55% by mass;

[0104] (b) an oxygen-containing oxidizer component of 10 to 85% by mass,
wherein a preferred aspect of the (b) component is (b-1) an oxidizer (at
least one oxidizer selected from a basic metal nitrate, a nitrate, and
ammonium nitrate) of preferably 10 to 85% by mass, more preferably 20 to
70%, and even more preferably 30 to 60% by mass, and (b-2) an oxidizer
(at least one oxidizer selected from a perchlorate and a chlorate) of
preferably 0.5 to 20% by mass, more preferably 1 to 10% by mass, and even
more preferably 1 to 5% by mass; and

[0105] (c) aluminum hydroxide of preferably 0.1 to 20% by mass, more
preferably 3 to 15% by mass, and even more preferably 4 to 10% by mass.

[0106] The following compositions, for example, may be used as this gas
generating agent.

[0118] A composition in which one or both of the following (d) component
and (e) component is blended with the aforementioned (a) to (c)
components may also be used:

[0119] (d) a binder of preferably no more than 20% by mass, more
preferably 0.5 to 10% by mass, and even more preferably 1 to 7% by mass;
and

[0120] (e) an additive selected from a metal oxide and a metal carbonate
of preferably no more than 20% by mass, more preferably 1 to 15% by mass,
and even more preferably 3 to 10% by mass.

[0121] The following compositions, for example, may be used as this gas
generating agent.

COMPOSITION EXAMPLE 4

[0122] (a) nitroguanidine

[0123] (b) a basic copper nitrate

[0124] (c) aluminum hydroxide

[0125] (d) guar gum

COMPOSITION EXAMPLE 5

[0126] (a) melanine

[0127] (b) a basic copper nitrate

[0128] (c) aluminum hydroxide

[0129] (d) sodium carboxymethylcellulose or guar gum

COMPOSITION EXAMPLE 6

[0130] (a) guanidine nitrate

[0131] (b) a basic copper nitrate

[0132] (c) aluminum hydroxide

[0133] (d) sodium carboxymethylcellulose or guar gum

[0134] The first and second gas generating agents having a lower
combustion temperature may be formed in a single-perforated cylindrical
form having an outer diameter of 1.2 to 6.0 mm and a length of 0.8 to 6.0
mm, and having a through hole having an inner diameter of 0.5 to 2.0 mm.

[0135] The gas generating agents shown below in Table 2 may be used as the
first and second gas generating agents with a low combustion temperature.

[0137] The first and second gas generating agents having a lower
combustion temperature preferably contain the following (a) to (c)
components, and also aluminum hydroxide serving as a coolant of 0.1 to
20% by mass, preferably 3 to 15% by mass, and more preferably 4 to 10% by
mass:

[0138] (a) guanidine nitrate serving as a fuel of 5 to 60% by mass,
preferably 10 to 60% by mass, and more preferably 10 to 55% by mass;

[0139] (b) a basic copper nitrate serving as an oxidizer of 10 to 85% by
mass, preferably 20 to 70% by mass, and more preferably 30 to 60% by
mass; and

[0140] (c) sodium carboxymethylcellulose serving as a binder of no more
than 20% by mass, preferably 1 to 15% by mass, and more preferably 3 to
10% by mass.

[0141] The respective gas generating agents may be used in the following
usage amounts (and the usage proportions corresponding to the usage
amounts), for example:

[0142] first gas generating agent with the higher combustion temperature:
0.5 to 15 g, preferably 1 to 15 g, and more preferably 1.5 to 15 g;

[0143] first gas generating agent with the lower combustion temperature: 3
to 150g, preferably 7 to 150 g, and more preferably 12 to 150 g;

[0144] second gas generating agent with the higher combustion temperature:
0.5 to 15 g, preferably 1 to 15 g, and more preferably 1.5 to 15 g; and

[0145] second gas generating agent with the lower combustion temperature:
1 to 50g, preferably 2 to 50 g, and more preferably 3 to 50 g.

[0146] In the gas generator of this embodiment, constituted as described
above, the gas generating agents 20b, 25b having a lower combustion
temperature are used in the first combustion chamber and second
combustion chamber, respectively, and hence the temperature of the gas
generated in each combustion chamber, and also the temperature of the gas
that is generated throughout the entire gas generator, can be reduced
dramatically in comparison with a case in which only gas generating
agents with a high combustion temperature are used. As a result, NOx
generation during combustion of the gas generating agents can be reduced,
and the filter 65 for purifying and/or cooling the combustion gas prior
to be discharged from the gas generator can be simplified.

[0147] In other words, in the gas generator shown in FIG. 1, the
cylindrical filter 65 is disposed between the first combustion chamber 20
and the peripheral wall of the housing 11 (i.e., a diffuser shell
peripheral wall 12b and a closure shell peripheral wall 13b) in order to
remove combustion residue from the combustion gas and cool the combustion
gas, but since the temperature of the gas generated throughout the entire
gas generator is suppressed to a low level, the filter 65 can be
simplified, for example having a greater porosity. Note that the filter
65 is disposed such that a gap 72 is formed between the filter 65 and the
peripheral wall of the housing 11.

[0148] Examples of the simplified cylindrical filter 65 include a filter
formed from thin metal wire (e.g., an iron wire or the like) with a wire
diameter of approximately 0.3 to 1.2 mm, wound into cylindrical form, a
filter formed by winding plan woven thin metal wire into multiple layers,
and then subjecting this to compression molding, a filter formed by
winding one or a combination of plain woven wire mesh, plain dutch woven
wire mesh, or twilled dutch woven wire mesh with a wire diameter of
approximately 0.3 to 0.8 mm, and a filter formed by inserting ceramic
fiber or metal fiber between these wire meshes.

[0149] The structure of the cylindrical filter is to be selected
appropriately in accordance with the type of gas generating agent in use,
the usage amount, differences in the usage proportion of gas generating
agents having different combustion temperatures, or in other words the
combustion temperature range, and the amount of combustion residue that
is produced. For example, when a gas generating agent having a lower
combustion temperature (e.g., approximately 1000 to 1700.degree. C.)
which produces little combustion residue is used, a cylindrical filter
having a bulk density of 1 to 5 g/cm.sup.3 or preferably 2 to 3
g/cm.sup.3, and a thickness of 3 to 10 mm or preferably 3 to 6 mm, may be
used.

[0150] The shielding plate 66 is disposed on the inside of the cylindrical
filter 65, and the aforementioned gap (first gap 71) is provided between
the cylindrical filter 65 and the tubular shielding plate 66 on the
inside thereof. Instead of this gap 71, however, part of the cylindrical
filter 65 which makes contact with the shielding plate 66 (this part
having approximately the same width as the gap) may be formed as a
rarefied structure having a large porosity, which in actuality is an
identical state to that in which the gap is provided. The rarefied
structure relates to the remaining dense structure having a small
porosity in such a manner that when the bulk density of the dense
structure is within the range described above, the bulk density of the
rarefied structure can be set at 0.1 to 11.0 g/cm.sup.3. The width of the
gap 71 or the rarefied structure portion secured between the cylindrical
filter 65 and the shielding plate 66 is preferably between 0.5 and 3 mm,
and more preferably between 1 and 2 mm.

[0151] By providing the shielding plate 66 covering the inside of the
cylindrical filter 65 and also a shielding plate (not shown) covering the
outside of the filter, the combustion gas filtering (e.g., combustion
residue filtering) and cooling effects can be further improved.

[0152] Note that the seal tape 75 closing the gas discharge holes 17, 18
may be set to rupture simultaneously or separately according to the
activation condition of the igniters (whether only one of the igniters is
activated, both are activated simultaneously, or the two igniters are
activated at a time difference).

[0153] Next, an operation of the gas generator 10 for an air bag,
performed when the two igniters are activated with a time difference,
will be described by referring to FIG. 1.

[0154] When the first igniter 31 is activated, the first gas generating
agent 20a having a higher combustion temperature is ignited and burned,
producing a gas (having energy to ignite unburned gas generating agents)
which ruptures the seal tape 60. The gas then passes through the first
through hole 51 provided in the peripheral wall of the inner cylinder 15,
and is thus discharged into the space outside the inner cylinder 15 in
the same first combustion chamber 20.

[0155] The gas ejected through the first through hole 51 collides with the
shielding plate 66 that opposes the first through hole 51, such that the
advancement direction of the gas changed to an upward direction, and thus
the first gas generating agent 20b having a lower combustion temperature,
which exists downstream with respect to the advancement direction, is
ignited and burned. In other words, the shielding plate 66 changes the
advancement direction of the gas from a radial direction to an axial
direction, such that the gas is supplied to the gas generating agent
existing in both the radial direction and the axial direction. As a
result, the ignitability and combustibility of all of the first gas
generating agent in the first combustion chamber 20 are improved.

[0156] If the shielding plate 66 was not provided, the gas ejected through
the first through hole 51 to the outside in the radial direction would be
supplied sufficiently to the first gas generating agent 20b existing in
the ejecting direction, but would be unlikely to reach the first gas
generating agent 20b existing above the first through hole 51. This
problem is particularly striking when a gas generating agent having a
poor ignitability is used. When the shielding plate 66 is used together
with the filter 65 in the manner described in this embodiment, however,
problems relating to the transmission efficiency of the gas can be
solved. Moreover, when the shielding plate 66 is used, the gas collides
with only part of the cylindrical filter 65, thus preventing damage to
the cylindrical filter 65. Accordingly, the axial position of the first
through hole 51 is to be adjusted so that these actions and effects can
be exhibited.

[0157] Note that the communicating hole 80 formed in the inner cylinder 15
between the first combustion chamber and second combustion chamber is
closed by the stainless steel seal tape 58, and hence the combustion gas
in the first combustion chamber 20 does not flow into the second
combustion chamber 25. All of the gas that is generated in the first
combustion chamber 20 passes through the filter 65, ruptures the seal
tape 75, and discharged into the air bag (not shown) through the gas
discharge ports 17, 18.

[0158] The gas generated by the combustion of the first gas generating
agents 20a, 20b enters the cylindrical filter 65 through the part not
covered by the shielding plate 66 (or through gas vents), whereupon part
of this gas travels through the cylindrical filter 65 as is in the axial
direction to reach the gap 72 at the outer periphery side of the filter
65. The remainder of the combustion gas travels into the gap 71 on the
inner periphery side of the filter 65, passes through the cylindrical
filter 65 in the radial direction, and thus reaches the gap 72 on the
outer periphery side of the filter 65. The combustion gas then ruptures
all or part of the seal tape 75, and is thus discharged through all or a
part of the gas discharge ports 17, 18, whereby the air bag is inflated.

[0159] By securing the gap 71 at the inner periphery side of the filter 65
defined by the shielding plate 66, the gas that passes through the gap 71
then passes through the cylindrical filter 65 in the axial direction. As
a result, the entire cylindrical filter 65 is used, and therefore the
contact time between the gas and the filter 65 is lengthened, enabling an
improvement in the combustion gas cooling and filtering effects.

[0160] The second igniter 32 is activated with a brief time difference
with the activation of the first igniter 31. The flame produced by an
activation of the second igniter 32 passes through the second through
hole 52, and advances directly into the second combustion chamber. When
the flame (having energy to ignite unburned gas generating agent) enters
the second combustion chamber, the second gas generating agent 25a having
a higher combustion temperature is first ignited and burned in the second
combustion chamber 25, whereupon the resulting flame causes the second
gas generating agent 25b having a lower combustion temperature to ignite
and burn. As described above, when the second gas generating agents are
burned, the opening area of the communicating hole 80 provided in the
upper portion of the inner cylinder 15 (or when the retainer 55 is
provided with an opening, the opening portion thereof) and the height
position at which the communicating hole 80 is formed have been adjusted.
Therefore, the flame circulates favorably through the entire second
combustion chamber 25, thus improving the ignitability and combustibility
of the second gas generating agent. When the communicating hole 80 is
closed by the seal tape 58, the initial combustibility of the second gas
generating agent is improved.

[0161] The gas generated in the second combustion chamber 25 is ejected
through the communicating hole 80 formed in the inner cylinder 15 in a
radial direction, and flows into the first combustion chamber 20. The gas
is then cooled and purified by the cylindrical filter 65 in a similar
manner to that described above, and then discharged through the gas
discharge holes 17, 18 to inflate the air bag further.

EXAMPLE

[0162] First Example

[0163] The gas generator for an air bag shown in FIG. 1 was manufactured.
The details are as follows.

[0170] First and second gas generating agents having a higher combustion
temperature

[0171] A pellet form with an outer diameter of 1.5 mm and a length of 1.5
mm, having the following composition (combustion temperature:
2200.degree. C.; generated gas amount: 2.5 mol/100 g):

[0172] nitroguanidine: 34.4% by mass;

[0173] strontium nitrate: 55.6% by mass; and

[0174] sodium carboxylmethylcellulose: 10.0% by mass.

[0175] First and second gas generating agents having a lower combustion
temperature

[0176] A single-perforated cylindrical form with a through hole, having an
outer diameter of 4.5 mm, an inner diameter of 1.2 mm, and a length of 4
mm, and having the following composition (combustion temperature:
1200.degree. C.)

[0177] guanidine nitrate: 41% by mass;

[0178] basic copper nitrate: 49% by mass;

[0179] sodium carboxylmethylcellulose: not more than 5% by mass; and

[0180] aluminum hydroxide: 5% by mass.

[0181] Note that in the embodiment and example described above,
description is based on a gas generator using two igniters. However, the
present invention is not limited to this number of igniters, and may be
applied to a gas generator with a single igniter or the like. In a gas
generator such as that shown in FIG. 1 of JP-A No. 10-95303, for example,
in which an inner cylinder is disposed inside a housing such that a
combustion chamber charged with a gas generating agent is formed at the
outside of the inner cylinder, an igniter is disposed in the lower side
of the space inside the inner cylinder, and a transfer charge is disposed
in the upper side, a gas generating agent having a higher combustion
temperature may be charged into the inner cylinder instead of the
transfer charge, and a gas generating agent having a lower combustion
temperature may be charged into the combustion chamber at the outside of
the inner cylinder.

[0182] The invention being thus described, it will be obvious that the
same may be varied in many ways. Such variations are not to be regarded
as a departure from the spirit and scope of the invention, and all such
modifications are intended to be included within the scope of the
following claims.